As a method for clamping an optical disc, there is a magnetic clamp system FIG. 6 shows an embodiment of an optical disc which is fixed by such a system. In FIG. 6, a pair of transparent substrates 1 made of a plastic are bonded to each other via a pair of spacers 3 in such a manner that recording films 2 are opposed to each other, magnet hubs 4 are fitted into an axle hole from upper and lower sides and the optical disc is inserted into the spindle of a disc drive at the time of use thereof and retained and fIxed by means of a magnet fixed to the spindle.
Conventional methods for fixing the magnet hub include a method wherein an annular metal plate 6 composed of a ferromagnetic substance and provided with a plurality of connecting rods 8 is abutted against one side of the plastic substrate, each connecting rod 5 is inserted into a corresponding hole formed in the substrate and a metal plate 7 is press-fitted onto the end part of each connecting rod, which protrude from the other side of the substrate as shown in FIG. 7 (see, Japanese Patent Laid-Open Publn. No. 119747/1987).
However, the above-described magnetic hub has such disadvantages that it has a complicated structure and must be worked with high accuracy and hence it is expensive and that the disc substrates must be perforated in fixing the magnet hub. Therefore fixing the magnetic hub to an optical disc is difficult.